J . Org. Chem. 1989,54, 6018-6021
6018
Scheme I11 TEST H --Co2Et
-5
v
OAc c
9 10
K-PH1
5HI 1
0
x=o
.c--
fi
OAc
11
X =aOAc;PH
0
(i) DiBAH c
1
(ii) Ph3P = CH (CH& QK
13
12
from 12. The overall yield of 1 from 3 is 27%. As previously described, 35J2is readily available in enantiomerically homogeneous form from cis-l,4-diacetoxycyclopentene. The stereochemical outcome a t C13 arising from the coupling of similar substrates under the same conditions is amazing. In the previously described aldols5leading to 5 and 6 no other stereoisomers were observed. Yet when the ynal 7 is employed 8 is the only product observed! Instead of offering ad hoc interpretations that do not flow from sound experimental observations, we prefer to outline an agenda of questions that must be addressed. Why does a particular substitution type on the aldehyde favor or disfavor silyl transfer? Is silyl transfer fundamental or accessory to the stereochemical outcome? Do the sharply differing results arise from a common transition-state ~~
~
(12) Cf: (a) Deardorff, D. R.; Myles, D. C.; MacFerrin, K . D. Tetrahedron Lett. 1985, 5615. (b) Deardorff, D. R.; Matthews, A. J.; McMeekin, D. S.;Craney, C. L. Ibid. 1986, 1255.
alignment differing in the placement of the R and H group of the aldehyde or do the reaction types differ in overall topography (chair vs boat, synclinal vs antiperiplanar)? Answers to these sorts of questions are not readily obtained but are crucial to illuminating this interesting stereochemical finding and extending it to new domains. I n the meantime, we note that the chemistry disclosed here and previously5 provides straightforward access to optically pure prostaglandins with complete control of the configuration at either C13or C15in any stereochemical sense.
Acknowledgment. This research was supported by PHS Grant HL25848. NMR Spectra were obtained through the auspices of the Northeast Regional NSF/ NMR facility at Yale University, which was supported by NSF Chemistry Division Grant CHE 7916210. Supplementary Material Available: Experimental procedures and characterization data for all compounds (5 pages). Ordering information is given on any current masthead page.
Rearrangements of Cyclobutenones. Conversion of Selected 4-Allylcyclobutenones to Bicycle[ 3.2.0lheptenones Simon L. Xu and Harold W . Moore* Department of Chemistry, University of California, Iruine, California 92717
Received October 9. 1989 Summary: 4-Allyl-4-alkoxy(or hydroxy or (trimethylsily1)oxy)cyclobutenones are reported to rearrange to bicyclo[3.2.0]hept-2-en-7-ones upon thermolysis in refluxing toluene. The synthetic scope and mechanism of this unusual transformation are discussed. The products are envisaged to arise from an electrocyclic ring opening of the cyclobutenones to the corresponding vinylketenes which 0022-3263/89/1954-6018$01.50/0
+
then undergo an intramolecular [ 2 21 cycloaddition of the ketene moiety to the nonconjugated allylic double bond.
Sir: Selected 4-alkynyl, 4-alkenyl-, and 4-arylcyclobutenones have recently been shown to undergo facile ring expansion to respectively benzoquinones, hydroquinones, 0 1989 American Chemical Society
Communications
J. Org. Chem., Vol. 54, No. 26, 1989 Scheme I'
and annelated hydroq~inones.l-~These transformations all have a mechanistic commonality in that the starting cyclobutenones experience a selective electrocyclic ring opening with outward rotation of the electron-donating group at 4-position to give the corresponding conjugated vinylketene~.~ These ketenes then undergo ring closure leading ultimately to the observed products. We now report that the corresponding nonconjugated vinylketenes can be generated from selected 4-allylcyclobutenones and these undergo facile intramolecular [2+ 21 cycloaddition of the ketene group to the nonconjugated allylic double bond, giving bicycl0[3.2.0]hept-2-en-7-ones.~~~ This is a synthetically useful reaction since the starting cyclobutenediones are readily prepared in a variety of substitution patterns, and, based upon analogy, the products are potentially versatile precursors to a number of other systems, including five-, six-, seven- and eight-membered rings.'*8
(1) For the conversion of 4-alkynylcyclobutenones to quinones and 2-alkylidene-1,3-cyclopentenediones, see: (a) Karlacon, J. 0.;Nguyen, N. V.; Foland, L. D.; Moore, H. W. J. Am. Chem. SOC. 1985,107,3392. (b) Decker, 0. H. W.; Moore, H. W. J. Org. Chem. 1987,52,1174. (c) Foland, L. D.; Karhon, J. 0.;Perri, S. T.; Schwabe,R.; Xu, S. L.; Patil, S.; Moore, H. W. J. Am. Chem. SOC. 1989,111, 975.
(2) For selected references to the conversion of 4-arylcyclobutenones to quinones, see: (a) Perri, S. T.; Foland, L. D.; Decker, 0. H.; Moore, H. W. J. Org. Chem. 1986,51,3067. (b) Liebeskind, L. S.; Iyer, S.; Jewell, C. F. J. Org. Chem. 1986, 51, 3065. (c) Perri, S. T.; Moore, H. W. Tetrahedron Lett. 1987,28,4507. (d) Reed, M. W.; Moore, H. W. J. Org. Chem. 1988,52,4166. (e) Foland, L. D.; Decker, 0. H. W.; Moore, H. W. J. Am. Chem. SOC. 1989,111,989. (3) For the conversion of 4-alkenylcyclobutenones to quinones, see: (a) Perri, S. T.; Dyke, H. J.; Moore, H. W. J. Org. Chem. 1989,54,2032. (b) Perri, S. T.; Moore, H. W. J.Am. Chem. SOC.,in press. (4) The selectivity of the electrocyclic ring opening is in agreement with the computational studies reported for the analogous ring opening of cyclobutenes. See: (a) Houk, K. N.; Spellmeyer, D. G.; Jefford, C. W.; Rimbault, C. G.; Wang, Y.; Miller, R. D. J. Org. Chem. 1988, 53, 2125. (b) Randan, N. G.; Houk, K. N. J. Am. Chem. SOC.1985, 107, 2099. (5) For an excellent review of intramolecular ketene/alkene cycloadditions, see: Snider, B. B. Chem. Reo. 1988,88, 793. (6) We are grateful to one of the reviewers who pointed out the recent independent study of the formation of a bicycloheptenone from 4,4-diallyl-2-methylcyclobutenone:Ernst, B.; de Mesmaeker, A.; Greuter, H.; Veenstra, S. J. In Strain and its Implication in Organic Chemistry; de Meijere, A,, Blechert, S., Eds.; Kluwer Academic Publishers: Boston, 1989; pp 221-222. (7) For the conversion of squaric acid to substituted cyclobutenedione, see: (a) Reed, M. W.; Perri, S. T.; Pollart, D. J.; Foland, L. D.; Moore, H. W. J. Org. Chem. 1988,53,2477. (b) Liebeskind, L. S.;Fengl, R. W.; Wirtz, K. R.; Shawe, T. T. J. Org. Chem. 1988, 53, 2482. Also, a convenient synthesis of substituted benzocyclobutenediones has recently been reported. See: Liebeskind, L. S.; Lescosky, L. J.; McSwain, C. M. J. Org. Chem. 1989, 54, 1435. (8)For selected examples of the conversion of bicyclo[3.2.0]heptanes to other ring systems, see the following. 5-membered ring systems: (a) Corey, E. J.; Kang, M.; Desai, M. C.; Ghosh, A. K.; Houpis, I. N. J.Am. Chem. SOC. 1988,110,649. (b) De Mesmaeker, A,; Veenstra, S. J.; E r s t , B. Tetrahedron Lett. 1988, 459. (c) Jackson, D. A,; Rey, M.; Dreiding, A. S. Tetrahedron Lett. 1983, 4817. (d) Matz, J. R.; Cohen, T. Tetrahedron Lett. 1981,2459. (e) Wenkert, E.; Arrhenius, T. S. J.Am. Chem. SOC. 1983,105,2030. 6-membered ring systems: (0 Cohen, T.; Bhupathy, 1983, 105, 520. (g) Bhupathy, M. M.; Matz, J. R. J. Am. Chem. SOC. 1983, 105, 6978. (h) Danheiser, R. L.; Cohen, T. J. Am. Chem. SOC. Martinez-Davila, C.; Sard, H. Tetrahedron 1981,37,3943. (i) Snider, B. B.; Niwa, M. Tetrahedron Lett. 1988, 3175. 7-membered ring systems: (j) Huston, R.; Rey, M.; Dreiding, A. S. Helu. Chim. Acta 1982,65,451. (k) Huston, R.; Rey, M.; Dreiding, A. S. Helu. Chim. Acta 1982,65,1563. (1) Hwang, C. S.; Reusch, W. Synthesis 1989, 428. (m) Oppolzer, W.; Wylie, R. D. Helu. Chim. Acta 1980,63, 1198. (n) Imafuku, K.; Arai, K. Synthesis 1989,501. &membered ring systems: (0) Gadwwd, R. C.; Lett, R. M. J. Org. Chem. 1982,47, 2268. (p) Gadwocd, R. C.; Lett, R. M.; 1986,108,6343. (4) Paquette, L. A.; Wissinger, J. E. J. Am. Chem. SOC. Colapret, J. A,; Andrews, D. R. J. Org. Chem. 1985, 50, 201. (r) Birch, A. M.; Pattenden, G. J. Chem. SOC.,Chem. Commun. 1980,1195. Norbornene ring system: ( 8 ) Wilson, S. R.; Mao, D. T. J.Chem. Soc., Chem. Commun. 1978, 479.
6019
"' 1
6CH;
2
CHpO CHlO CH;O 5
R
4
941
bCH;
*3
%I
a
-0CHp
71
89
83
b
-n-C4H9
27
89
85
c
-CH-CH2
53
87
90
d
-c6Hs
58
95
86
e
--n-CIHq
42
80
72
-
'(a) Allylmagnesium bromide/THF, -100 "C; (b) CHJ, Ag,O, K,CO3/CHSCN, room temperature; (c) toluene, 110 "C. Scheme I1
6
Za
CHpO
7 (CH&iiO
% H 56-c
CH30
OSi(CH;); 8
9
Specific examples of this transformation are given in Scheme I. The starting cyclobutenediones la-e were converted to the corresponding 4-allyl-3,4-dimethoxycyclobutenones 3a-e upon treatment with allylmagnesium bromide followed by 0-alkylation of the resulting 4hydroxycyclobuten-1-ones2a-e with methyl i ~ d i d e . ~ Thermolysis of 3a-e in refluxing toluene then gave the bicyclo[3.2.0]heptenones 5a-e in excellent yields via the proposed ketene intermediates 4a-e. The structure assignments of 5a-e as well as of 2a-e and 3a-e are based upon characteristic spectral data which are provided in Table I. Additional examples of this unusual ring expansion are given in Scheme 11. For example, it was of interest to see ~~
(9) Treatment of dimethyl s q u a r a z l a with Grignard reagents has previously been reported to give 1,4-additionrather than 1,a-adducts. see: Kraus, J. L. Tetrahedron Lett. 1985, 26, 1867. However, with allylmagnesium bromide, as noted here, the reaction proceeds to give the l,a-adduct 2a (71% ) along with the diadduct in which allyl groups have added to both carbonyl moieties (15%).
6020 J. Org. Chem., Vol. 54, No. 26, 1989 compd
2a
2b
2c
2d
2e
3a
3b
3c
3d
3e
5a
5b
5c
5d
5e
Communications
Table I. Physical Properties of Compounds 2-10"* NMR (CDCI,), 6 IH 2.44 (9, 1 H), 2.61 (d, J = 9.0 Hz, 1 H), 3.96 (9, 3 H), 4.14 (s, 3 H), 5.19 (d, J = 12.0 Hz, 1 H), 5.21 (d, J = 15.0 Hz, 1 H), 5.78-5.93 (m, 1 H); 13C 37.51, 58.30, 60.00, 85.50, 119.00, 131.92, 133.51, 167.95, 186.81 oil lH 0.89 (t,J = 7.5 Hz, 3 H), 1.26-1.38 (m, 2 H), 1.43-1.54 (m, 2 H), 2.04-2.15 (m, 2 H), 2.58 (dd, J = 14.1, 7.4 Hz, 1 H), 2.67 (dd, J = 14.1, 7.4 Hz, 1 H), 2.77 (s, 1 H), 4.12 (s,3 H), 5.13-5.23 (m, 2 H), 5.73-5.87 (m, 1 H); 13C 13.54, 21.42, 22.32, 29.57, 37.61, 59.22, 90.39, 118.67, 127.17, 132.09, 183.43, 193.82 oil lH 2.58-2.73 (m, 2 H), 4.19 (9, 3 H), 5.15-5.25 (m, 2 H), 5.39 (dd, J = 11.0, 2.0 Hz, 1 H), 5.76-5.90 (m, 1 H), 5.96 (dd, J = 17.6, 2.0 Hz, 1 H), 6.18 (dd, J = 18.0, 11.0 Hz, 1 H); 13C 37.88, 60.03, 90.73, 119.26, 121.51, 121.71, 123.35, 131.71, 180.70, 191.09 101-104 lH 2.73 (ddt, J = 14.2, 7.2, 1.0 Hz, 1 H), 2.85 (s, 1 H), 2.87 (ddt, J = 14.2, 7.6, 1.0 Hz, 1 H), 4.27 (s, 3 H), 5.15-5.30 (m, 2 H), 5.78-5.92 (m, 1 H), 7.26-7.40 (m, 3 H), 7.70-7.73 (m, 2 H); 13C 38.53, 59.98, 92.11, 119.20, 124.07, 126.91, 128.00, 128.24, 128.33, 131.79, 181.94, 190.95 lH 0.91 (t, J = 7.2 Hz, 3 H), 1.40-1.60 (m, 4 H), 2.33 (t, J = 7.0 Hz, 57-58 2 H), 2.60 (d, J = 7.4 Hz, 2 H), 2.67 (s, 1 H), 4.33 (s, 3 H), 5.17-5.25 (m, 2 H), 5.76-5.90 (m, 1 H); 13C 13.46, 19.11, 21.91, 30.23, 37.32, 60.76, 66.91, 90.09, 95.46, 108.22, 119.38, 131.30, 184.60, 190.07 oil IH 2.54 (dd. J = 14.4. 7.5 Hz. 1 H). 2.63 (dd. J = 14.4. 7.2 Hz. 1 H). ,, 3.33 (s, 3'H), 3.97 (s, 3 H),'4.12'(s, 3 H), 5:10-5.15 (m, 1 H), 5.70-5.84 (m, 1 H); 13C 36.51, 51.81, 58.28, 59.69, 91.42, 118.25, 132.01, 134.59, 167.03, 185.89 oil 'H 0.90 (t, J = 7.2 Hz, 3 H), 1.30-1.40 (m, 2 H), 1.45-1.55 (m, 2 H), 2.10-2.16 (m, 2 H), 2.51 (ddt, J = 14.4, 7.6, 1.0 Hz, 1 H), 2.69 (ddt, J = 14.4, 7.0, 1.2 Hz, 1 H), 3.34 (s, 3 H), 4.10 (s, 3 H), 5.06-5.17 (m, 2 H), 5.65-5.79 (m, 1 H); 13C 13.51, 21.45, 22.39, 29.72, 36.92, 52.38, 58.98, 96.71, 118.28, 129.15, 132.19, 182.44, 191.79 'H 2.55 (ddt, J = 14.4, 7.6, 1.0 Hz, 1 H), 2.71 (ddt, J = 14.4, 7.0, 1.2 Oil Hz, 1 H), 3.36 (8, 3 H), 4.16 (9, 3 H), 5.07-5.18 (m, 2 H), 5.40 (dd, J = 11.0, 2.1 Hz, 1 H), 5.69-5.83 (m, 1 H), 5.97 (dd, J = 17.6, 2.1 Hz, 1 H), 6.17 (dd, J = 17.6, 11.0 Hz, 1 H); 13C 37.10, 52.80, 59.78, 96.97, 118.60, 121.40, 121.67, 124.84, 131.83, 180.23, 189.86 oil lH 2.64 (ddt, J = 14.5, 7.7, 1.0 Hz, 1 H), 2.90 (ddt, J = 14.5, 7.0, 1.3 Hz, 1 H), 3.43 (s, 3 H), 4.23 (s, 3 H), 5.08-5.23 (m, 2 H), 5.71-5.85 (m, 1 H), 7.26-7.36 (m, 3 H), 7.75-7.80 (m, 2 H); 13C 37.87, 52.91, 59.73, 98.37, 118.84, 125.54, 126.97, 128.06, 128.15, 128.42, 131.83, 181.16, 188.97 oil IH 0.91 (t,J = 7.2 Hz, 3 H), 1.38-1.60 (m, 4 H), 2.35 (t,J = 6.9 Hz, 2 H), 3.34 (s, 3 H), 4.33 (s, 3 H), 5.1e5.18 (m, 2 H), 5.69-5.83 (m, 2 H); 13C 13.50, 19.18, 21.97, 30.28, 36.48, 53.02, 60.59, 66.77, 95.67, 96.55, 109.72, 118.83, 131.59, 184.73, 189.57 oil lH 2.30 (d, J = 16.2 Hz, 1 H), 2.55-2.70 (m, 2 H), 2.90 (dd, J = 16.2, 7.0 Hz, 1 H), 3.10 (dd, J = 17.4, 9.1 Hz, 1 H), 3.32 (s, 3 H), 3.68 (s, 3 H), 3.81 (s, 3 H); 13C 26.29, 32.74, 47.89, 52.21, 57.19, 58.34, 103.30, 127.54, 142.10, 203.85 lH 0.90 (t, J = 7.2 Hz, 3 H), 1.20-1.35 (m, 4 H), 1.65-1.75 (m, 2 H), oil 2.30 (d, J = 15.4 Hz, 1 H), 2.30-2.38 (m, 1 H), 2.80 (dd, J = 15.7, 8.1 Hz, 1 H), 2.89 (dd, J = 18.1, 5.6 Hz, 1 H), 3.18 (dd, J = 17.9, 8.6 Hz, 1 H), 3.65 (s, 3 H), 3.71 (s, 3 H); I3C 13.89, 22.87, 25.07, 26.34, 28.15, 33.18, 51.07, 57.24, 58.79, 77.44, 131.60, 138.12, 209.98 lH 2.33 (d, J = 15.7 Hz, 1 H), 2.45-2.53 (m, 1 H), 2.85-2.96 (m, 2 H), oil 3.27 (dd, J = 18.1, 9.1 Hz, 1 H), 3.64 (s, 3 H), 3.74 (s, 3 H), 5.25 (d, J = 10.7 Hz, 1 H), 5.38 (d, J = 16.1 Hz, 1 H), 5.97 (dd, J = 17.5, 10.7 Hz, 1 H); 13C 27.49, 32.75, 50.98, 57.26, 58.85, 78.71, 116.68, 131.63, 133.12, 138.53, 206.67 oil 'H 2.42 (d, J = 15.9 Hz, 1 H), 2.62-2.66 (m, 1 H), 3.00-3.07 (m, 2 H), 3.35 (dd, J = 18.1, 9.2 Hz, 1 H), 3.53 (9, 3 H), 3.78 (s, 3 H), 7.26-7.39 (m, 5 H); 13C 29.90, 33.07, 51.47, 57.42, 59.05, 79.73, 126.20, 127.25, 128.55, 132.64, 137.81, 139.20, 206.68 'H 0.88 (t, J = 7.5 Hz, 3 H), 1.33-1.51 (m, 4 H), 2.20-2.30 (m, 3 H), oil 2.55-2.61 (m, 1 H), 2.91 (dd, J = 15.7, 8.1 Hz, 1 H), 2.98 (dd, J = 18.3, 5.9 Hz, 1 H), 3.35 (dd, J = 18.3, 9.2 Hz, 1 H), 3.70 (s, 3 H), 13.55, 18.74, 21.88, 29.21, 30.64, 33.01, 52.14, 57.31, 3.73 (9, 3 H); 59.03, 68.80, 74.02, 89.36, 129.99, 138.42, 201.85 'H 2.45 (dd, J = 18.4, 6.7 Hz, 1 H), 2.53 (d, J = 17.4 Hz, 1 H), 79-82 2.92-3.14 (m, 2 H), 3.18-3.27 (m, 1 H), 3.49 (s, 3 H), 3.56 (s, 3 H), 4.12 (s, 1 H); 13C 27.53, 41.55, 46.79, 53.69, 88.01, 101.70, 201.73, 209.36 139-141 'H 2.27 (dd, J = 18.7, 3.0 Hz, 1 H), 2.53 (dd, J = 15.8, 14.1 Hz, 1 H), 2.79 (dd, J= 18.7, 6.5 Hz, 1 H), 3.08 (dd, J = 15.8, 3.0 Hz, 1 H), 3.33-3.43 (m, 1 H), 4.17 (s, 3 H), 7.50 (td, J = 9.3, 1.2 Hz, 1 H), 7.65 (td, J = 8.1, 1.2 Hz, 1 H), 8.13 (d, J = 6.3 Hz, 1 H), 8.58 (d, J = 7.8 Hz, 1 H); 13C 33.39, 40.31, 45.27, 58.37, 127.56, 128.27, 130.05, 131.75, 134.00, 134.90, 143.86, 151.46, 195.65, 200.97 I
MS IR. cm-' 185 (100, CI) 3380, 3020, 2960, 1780, 1630, 1470, 1440, 1350, 1240, 1050, 1000, 930, 890, 870 210 (3, EI) 3460, 2970, 2940, 2880, 1760, 1750, 1620, 1610, 1465, 1360, 1090, 1000,920 181 (100, CI) 3380, 2980, 1760, 1750, 1650, 1590, 1470, 1360, 1090, 1000, 930, 740 231 (100, CI) 3330, 3000, 1760, 1635, 1600, 1500, 1470, 1450, 1370, 1320, 1010, 1000,690 235 (100, CI) 3370, 2960, 2940, 2880, 2240, 1770, 1615, 1460, 1360, 1240, 990,930, 640 199 (100, CI) 2990, 2960, 2840, 1780, 1650, 1470, 1440, 1350, 1225, 1140, 1120, 1055, 1020, 1000, 950, 930,890,850 224 (7, EI) 2970, 2950, 2880, 1770, 1635, 1625, 1470, 1460, 1360, 1290, 1120, 1000,930 194 (3, EI) 3000, 2960, 2840, 1760, 1650, 1590, 1470, 1460, 1410, 1360, 1300, 1140, 1120, 1000, 930 244 (13, EI) 3000, 2960, 2840, 1760, 1630, 1600, 1500, 1365, 1340, 1320, 1140, 1120, 1100, 1000, 790, 700, 620 248 (9, EI) 2970, 2940, 2240, 1775, 1650, 1640, 1470, 1460, 1360, 1130, 990, 930, 720 170 (19, EI) 2990, 2960, 2860, 1785, 1770, 1680, 1470, 1460, 1300, 1260, 1235, 1150, 1100, 1075, 1020, 1000, 800 224 (3, EI) 2960, 2940, 2860, 1780, 1675, 1465, 1390, 1335, 1290, 1255, 1230, 1220, 1160, 1090, 1080, 1025, 1000 194 (20, EI) 2980, 2940, 2850, 1780, 1770, 1680, 1465, 1455, 1340, 1300, 1260, 1240, 1100, 1000, 930 244 (HR) 2960, 2860, 1775, 1680, 1500, 1450, 1395, 1340, 1310, 1260, 1240, 1080, 760, 700 249 (100, CI) 2970, 2950, 2870, 1790, 1680, 1470, 1400, 1340, 1300, 1260, 1230, 1180, 1100, 1075, 1030, 1000 156 (5, EI) 3040, 3020, 2970, 2940, 2840, 1790, 1765, 1465, 1400, 1300, 1240, 1160, 1130, 1100, 1025, 650 228 (89, EI) 3040, 3020, 2960, 1710, 1700, 1625, 1600, 1450, 1370, 1330, 1290, 1260, 1135, 1085, 985, 800
J. Org. Chem., Vol. 54, No. 26, 1989 6021
Communications
Table 1 (Continued) compd mp,OC NMR (CDC13),8 IR, cm-' MS 'H 0.18 (s, 9 H), 2.62 (dd, J = 14.4,7.8 Hz, 1 H), 2.85 (dd, J = 14.4, 2960,1760,1630,1600,1500, 302 (8,EI) 8 oil 1450,1370, 1260,1120,1O00, 6.9 Hz, 1 H),4.24 (s, 3 H), 5.07 (d, J = 10.0 Hz, 1 H), 5.15 (dd, J = 930,890,850,770,760,700 17.0, 1.4 Hz, 1 H), 5.68-5.76 (m, 1 H), 7.25-7.37 (m, 3 H), 7.72-7.74 (m, 2 H); 13C 40.06,59.63,93.96,118.60,126.88,127.93,128.43, 132.22,181.86,189.02 9 oil 'H 0.26 (s, 9 H), 2.29 (d, J = 16.0 Hz, 1 H), 2.57-2.62 (m, 1 H), 2.93 (dd, 2970,2920,2860, 1770,1680, 303 (100,CI) 1400,1450,1390,1340,1300, J = 15.5,7.5 Hz, 1 H), 3.02 (dd, J = 18.0,5.5 Hz, 1 H), 1250,1100,1075,930,870, 3.35 (dd, J = 18.0,9.0 Hz, 1 H), 3.51 (9, 1 H), 7.24-7.27 850,760,700 (m, 2 H), 7.32-7.38 (m, 3 H);13C 0.55,30.45,36.35,51.50,58.32, 79.14,126.16,127.19,128.57,134.48,134.96,138.05,206.83 2980,2920,2840, 1780,1760, 230 (7,EI) 10 oil 'H 2.63 (d, J = 17.9 Hz,1 H), 2.89 (dd, J = 17.9,5.1 Hz), 1 H), 3.06 1600,1490, 1450,1410,1390, (dd, J = 17.6,7.7 Hz, 1 H), 3.27-3.50 (m, 2 H), 3.54 (s, 3 H), 4.01 1210,1140, 1130,1080,1050, (s, 1 H), 7.31-7.48 (m, 5 H) 1040,760,700 Elemental analysis data for 2a, 2d, 2e, 6, and 7 are in accord with the proposed structures. compounds are in accord with the proposed structures.
if the direct precursors to 3, i.e., 4-allyl-4-hydroxycyclobutenones, would undergo analogous ring expansion and thus provide a regiospecific route to bicyclo[3.2.0]heptane-3,g-diones. To this end, the thermolysis of 2a (toluene) was investigated and gratifyingly the bicycloheptanedione 6 was isolated in 65% yield. Nuclear magnetic resonance analysis of the crude reaction mixture showed the presence of the diastereomer of 6 as a minor product, and this could be converted to 6 upon treatment with silica gel. The structure of 6 is based upon standard spectral data (Table I) as well as upon a complete X-ray crystallographic structure determination, which clearly reveals the methoxy groups to be trans to one another. The above synthesis of bicyclo[3.2.0]heptanediones is limited in scope as shown by the fact that the 2-substituent of the starting cyclobutenones plays a dominant role in the course of the reaction. In this regard, 4-allyl-4-hydroxy3-methoxy-2-phenylcyclobutenone(2d) did not give a bicycloheptanedione as an insolatable product but rather gave 7 (42%) when subjected to the same reaction conditions used for the conversion of 2a to 6.1° This is a particularly unusual transformation and involves an overall dehydrogenation in addition to the molecular reorganization. Evidence concerning the mechanism of the conversion of 2d to 7, as well as an example extending the synthetic scope of the allylcyclobutenone rearrangement, was obtained from an investigation of the thermolysis of 4-allyl-3-methoxy-2-phenyl-4-( (trimethylsilyl)oxy)cyclobutenone (8). Here, a high yield (89%) of the bicycloheptenone 9 was realized. Desilylation of 9 upon treatment with CsF gave 10 (71%) as a 8:l mixture of diastereomers. It was found that 10 was stable when subjected to the thermolysis in refluxing toluene (conditions used for the rearrangement of 2d to 7) but was converted to 7 (31%) in refluxing toluene in the presence of a few drops of glacial acetic acid." This transformation is envisaged to involve the initial formation of the bicycloheptanedione10, which then undergoes an acid-catalyzed l,&acyl group migration to give 13 via the carbocation intermediates 11 and 12.12 Dehydrogenation of 13 and/or one of its possible tautomeric isomers under the reaction conditions would then (10) The structure of 7 is based upon the spectral data given in Table I as well as upon a complete X-ray crystallographic analysis. (11) Two other products, tentatively assigned as 2-methoxy-3phenyl-4-methylcyclopentenonesand 2-methoxy-3-phenyl-5-methylcyclopentenone, were also isolated in 15% and 12% yields. (12)Previously reported 1,3-acyl group migrations in the bicyclo[3.2.O]heptanone series have been reported but require high temperature or photolysis. See, for example: (a) Bertrand, M.; Gill, G.; Junino, A.; Maurin, R. Tetrahedron Lett. 1977,1779.(b) Lyle, T.A.; Frei, B. Helu. Chim. Acta 1981,64,2598.(c) Lyle, T. A.; Mereyala, H. B.; Pasual, A.; Frei, B. Helu. Chim. Acta 1984,67,774.
High-resolution mass spectra data for all
Scheme I11
11
10
12
13
7
provide the observed product 7 (Scheme 111). Presumably, the thermolysis of 2d results in the formation of 10 and that sufficient acid is also generated to induce the rearrangement of 10 to 7. In summary, 4-allyl-4-alkoxy(or hydroxy or sily1oxy)cyclobutenones, available in a variety of substitution patterns, rearrange to bicyclo[3.2.0]heptenones in good to excellent yields upon thermolysis in refluxing toluene. It ring system is noted that the bicyclo[3.2.0]hept-2-en-7-one is rare, particularly in highly functionalized forms.5 Clearly, its synthesis as outlined here has advantages over other known methods. Also, this transformation compliments earlier reports describing the ring expansion of appropriately substituted cyclobutenones to quinones, hydroquinones, annelated hydroquinones, and 2-alkylidene-1,3-cyclopentenediones.1-3J3 Extension of these studies to include the intramolecular ketene cycloadditions to substituted allylic groups as well as to higher homologues will be reported in due course. Acknowledgment. We thank the National Institutes of Health (Grant GM-36312) for financial support of this work. We are also grateful to Catherine A. Moore for technical assistance in obtaining mass spectral data and to Joseph Ziller for the X-ray crystallographic structure determination of compounds 6 and 7. (13) Liebeskind, L. S.; Mitchell, D.; Foster, B. S.J. Am. Chem. SOC.
1987,109,7908.
